This invention relates generally to the field of sex selection in mammalian offspring. It is especially relevant to the aspect of low dose artificial insemination for creating the desired sex of offspring. Particularly, the invention relates to systems for sorting sperm via flow cytometry for sex-specific and low dose efforts at artificial insemination or the like.
For ages it has been desired to select the sex of specific offspring. Beyond obvious psychological aspects, the actual sex selection of mammalian offspring has significant economic consequences when one considers its application to food producing animals such as cattle as well as celebrated trophy animals such as horses and the like. This great desire has resulted in a significant variety of efforts to achieve sex-selected offspring. Probably the effort which has appeared most likely to achieve the desired results has been efforts at sorting and selecting between X and Y sperm prior to insemination.
One of the challenges that effort at sorting X and Y sperm has faced is the large numbers of sperm involved. In natural insemination sperm are produced in some species by the billions; in artificial insemination less, but still significantly large numbers of sperm are used. For instance, artificial insemination techniques commonly use ten million to five hundred million sperm (depending on species). Thus a significant number of sperm are necessary even in an artificial insemination environment.
Many methods have been attempted to achieve the separation of X- and Y-chromosome bearing sperm. These methods have ranged from magnetic techniques such as appears disclosed in U.S. Pat. No. 4,276,139 to columnar techniques as appears disclosed in U.S. Pat. No. 5,514,537 to gravimetric techniques as discussed in U.S. Pat. No. 3,894,529, reissue U.S. Pat. No. 32350, U.S. Pat. Nos. 4,092,229, 4,067,965, and 4,155,831. Electrical properties have also been attempted as shown in U.S. Pat. No. 4,083,957 as well as a combination of electrical and gravimetric properties as discussed in U.S. Pat. Nos. 4,225,405, 4,698,142, and 4,749,458. Motility efforts have also been attempted as shown in U.S. Pat. Nos. 4,009,260 and 4,339,434. Chemical techniques such as those shown in U.S. Pat. Nos. 4,511,661 and 4,999,283 (involving monoclonal antibodies) and U.S. Pat. Nos. 5,021,244, 5,346,990, 5,439,362, and 5,660,997 (involving membrane proteins), and U.S. Pat. Nos. 3,687,803, 4,191,749, 4,448,767, and 4,680,258 (involving antibodies) as well as the addition of serum components as shown in U.S. Pat. No. 4,085,205. While each of these techniques has been presented as if to be highly efficient, in fact at present none of those techniques yield the desired level of sex preselection.
At present, the only quantitative technique used to achieve the separation of X -and Y-chromosome bearing sperm has been that involving individual discrimination and separation of the sperm through the techniques of flow cytometry. This technique appeared possible as a result of advances and discoveries involving the differential dye absorption of X- and Y- chromosome bearing sperm. This was discussed early in U.S. Pat. No. 4,362,246 and significantly expanded upon through the techniques disclosed by Lawrence Johnson in U.S. Pat. No. 5,135,759. The Johnson technique of utilizing flow cytometry to separate X- and Y-chromosome bearing sperm has been so significant an advancement that it has for the first time made the commercial separation of such sperm feasible. While still experimental, separation has been significantly enhanced through the utilization of high speed flow cytometers such as the MoFlo.RTM. flow cytometer produced by Cytomation, Inc. and discussed in a variety of other patents including U.S. Pat. Nos. 5,150,313, 5,602,039, 5,602,349, and 5,643,796 as well as international PCT patent publication WO 96/12171. While the utilization of Cytomation's MoFlo.RTM. cytometers has permitted great increases in speed, and while these speed increases are particularly relevant given the high number of sperm often used, certain problems have still remained. In spite of the almost ten-fold advances in speed possible by the MoFlo.RTM. flow cytometer, shorter and shorter sorting times have been desired for several reasons. First, it has been discovered that as a practical matter, the sperm are time-critical cells. They loose their effectiveness the longer they remain unused. Second, the collection, sorting, and insemination timings has made speed an item of high commercial importance. Thus, the time critical nature of the sperm cells and the process has made speed an essential element in achieving high efficacy and success rates.
Other problems also exist ranging from the practical to the theoretical. On the practical side, it has been desired to achieve sex-sorted sperm samples using inexpensive disposable components and substances. Also on the expense side, it has been desired to be able to achieve sorting (as well as collection and insemination) in as efficient a labor event as possible. Thus, for commercial production and success in this field, improvements which might only represent an increase in efficiency may still be significant. Related to the practical aspect of expense, is the practical aspect of the delicateness and sensitivity of the entire process. In this regard, it has been desired to simplify the process and make it as procedurally robust as possible so that operator error or skill can play an ever decreasing role.
In addition to the delicateness of the process, it has always been known that the sperm themselves are extremely delicate cells. While this factor at first glance seems like it might be considered easily understood, in fact, the full extent of the cells' sensitivities have not yet been fully explored. In the context of flow cytometry in general, most sorted cells or particles have often been spherical or otherwise physically able to withstand a variety of abuses. This is not the case for sperm cells. In fact, as the present invention discloses, the processing through normal flow cytometer techniques may, in fact, be unacceptable for cytometric sorting of sperm cells in certain applications. The sensitivities range from dilution problems and the flow cytometer's inherent need to isolate and distinguish each cell individually as well as the pressure and other stresses which typical flow cytometry has, prior to the present invention, imposed upon the cells or other substances that it was sorting. This may also represent a unique factor for sperm cells because it appears that even though the sperm cell may appear to pass through the flow cytometer and be sorted with no visually discernable side-effects, in fact, the cells themselves may have been stressed to the point that they perform less than optimally in the insemination process. Thus, an interplay of factors seems involved and has raised unusual problems from the perspective of sperm cell sorting and ultimate use for artificial insemination.
Another problem which has remained--in spite of the great advances achieved through the Johnson patent and related technology--is the fact that prior to the present invention it has been extremely difficult to achieve lower dosage insemination with sexed sperm. While historically, some achievement of low dose insemination has occurred, it has appeared to be more on a theoretical or laboratory environment rather than from environments which are likely to be experienced in or applicable to a commercial application. In this regard, the desire has not been merely to achieve low dose insemination but rather to achieve low dose insemination with pregnancy success rates which are comparable to existing unsexed, high dosage artificial insemination efforts. Thus, the advances achieved by the present inventors in both sexed and low dose artificial insemination represent significant advances which may, for the first time, make commercial applications feasible.
Another problem which has been faced by those in the industry--again, in spite of the great advances by the Johnson patent and related technology--is the fact that the problem itself, namely, artificial insemination with a high success rate is one of a statistical nature in which a multitude of factors seem to interplay. Thus, the solutions proposed may to some degree involve a combination of factors which, when thoroughly statistically studied, will be shown to be necessary either in isolation or in combination with other factors. Such a determination is further compounded by the fact that the results themselves vary by species and may be difficult to ascertain due to the fact that testing and statistical sampling on a large enough data base is not likely to be worth the effort at the initial stages. For these reasons the invention can also involve a combination of factors which may, individually or in combination, represent the appropriate solutions for a given application. This disclosure is thus to be considered broad enough so that the various combinations and permeations of the techniques disclosed may be achieved. Undiscovered synergies may exist with other factors. Such factors may range from factors within the sorting or flow cytometer steps to those in the collection as well as insemination steps. At present, studies have been primarily achieved on bovine species, however, it is not believed that these techniques will be limited to such species or, for that matter to only sperm cells. It appears that the techniques used may have application beyond just sperm cells into areas which involve either sensitive items to be sorted or merely minimization of the impacts of the stresses of flow cytometry upon the item sorted.
Interestingly, while the present invention takes an approach to minimize the impacts and stresses upon the sperm cells, others appear to have actually taken steps away from this direction by increasing pressures and demands for speed and other such performance. Essentially, the drive for low dose insemination and high speed processing may, in an individual or perhaps interrelated fashion have posed problems which limited one another. Thus, while there has been a long felt but unsatisfied need for high speed, low dose sexed insemination, and while the implementing arts and elements have long been available, prior to the present invention the advances or perhaps combinations of advances had apparently been overlooked by those skilled in the art. Perhaps to some degree they failed to appreciate that the problem involved an interplay of factors as well as peculiar necessities for the types of cells (sperm cells or perhaps species-specific sperm cells) involved in this field. Interestingly, as the listing of efforts earlier in this discussion shows, substantial attempts had been made but they apparently failed to understand the problem inherent in such an area as low dose, sexed insemination and had perhaps assumed that because the natural service event involves perhaps billions of sperm, there may have been physical limitations to the achievement of artificial insemination with numbers which are as many as four orders of magnitude less in number. Thus, it may not be surprising that there was to some extent an actual teaching away from the technical direction in which the present inventors went. Perhaps the results may even be considered unexpected to a degree because they have shown that sexed, low dose artificial insemination can be achieved with success rates comparable to those of unsexed, high dose artificial insemination. It might even be surprising to some that the techniques and advances of the present invention in fact combine to achieve the great results shown. While each technique could, in isolation, be viewed by some as unremarkable, in fact, the subtle changes appear to afford significant advances in the end result--whether considered alone or in combination with other subtle changes.
Thus, until the present invention the achievement of success rates for low dose, sexed artificial insemination has not been possible with levels of performance necessary or simplified procedures likely to be necessary to achieve commercial implementation. The present invention discloses techniques which permit the achievement of improved performances and thus facilitate the end result desired, namely, low dose, sexed artificial insemination on a commercial basis.